Yeah, I get thoughts in my head, like I'm day dreaming in a way, and I laugh when I say something funny inside. Sometimes I imagine conversing and saying something with people I like in my head, but unable to do it in real, or it just goes wrong.
I have laughed in public a few times, i.e in a bus full of people or back in school and college, and embarrassingly got caught once ir twice.... And today in a shop kept smiling like a treasure cat until I noticed the CCTV camera...

oops I don't always do it though, but when I do, I do...